MIR164B ensures robust Arabidopsis leaf development by compensating for compromised POLYCOMB REPRESSIVE COMPLEX2 function.

Robustness is pervasive throughout biological systems, enabling them to maintain persistent outputs despite perturbations in their components. Here, we reveal a mechanism contributing to leaf morphology robustness in the face of genetic perturbations. In Arabidopsis (Arabidopsis thaliana), leaf shape is established during early development through the quantitative action of the CUP-SHAPED COTYLEDON2 (CUC2) protein, whose encoding gene is negatively regulated by the co-expressed MICRORNA164A (MIR164A) gene.

A fully sequenced collection of homozygous EMS mutants for forward and reverse genetic screens in Arabidopsis thaliana.

Genetic screens are powerful tools for biological research and are one of the reasons for the success of the thale cress Arabidopsis thaliana as a research model. Here, we describe the whole-genome sequencing of 871 Arabidopsis lines from the Homozygous EMS Mutant (HEM) collection as a novel resource for forward and reverse genetics. With an average 576 high-confidence mutations per HEM line, over three independent mutations altering protein sequences are found on average per gene in the collection.

A CUC1/auxin genetic module links cell polarity to patterned tissue growth and leaf shape diversity in crucifer plants.

How tissue-level information encoded by fields of regulatory gene activity is translated into the patterns of cell polarity and growth that generate the diverse shapes of different species remains poorly understood. Here, we investigate this problem in the case of leaf shape differences between , which has simple leaves, and its relative that has complex leaves divided into leaflets. We show that patterned expression of the transcription factor CUP-SHAPED COTYLEDON1 in (ChCUC1) is a key determinant of leaf shape differences between the two species.

Model-based reconstruction of whole organ growth dynamics reveals invariant patterns in leaf morphogenesis.

Plant organ morphogenesis spans several orders of magnitude in time and space. Because of limitations in live-imaging, analysing whole organ growth from initiation to mature stages typically rely on static data sampled from different timepoints and individuals. We introduce a new model-based strategy for dating organs and for reconstructing morphogenetic trajectories over unlimited time windows based on static data.

Substitutes for to Form Complex Leaves and Petals.

LEAFY plant-specific transcription factors, which are key regulators of flower meristem identity and floral patterning, also contribute to meristem activity. Notably, in some legumes, LFY orthologs such as Medicago truncatula SINGLE LEAFLET (SGL1) are essential in maintaining an undifferentiated and proliferating fate required for leaflet formation. This function contrasts with most other species, in which leaf dissection depends on the reactivation of KNOTTED-like class I homeobox genes (KNOXI).

The NGATHA-like Genes and Are Not Required for Stem Cell Specification during Embryo Development in .

In plants, stem cells are embedded in structures called meristems. Meristems can be formed either during embryogenesis or during the plant's life such as, for instance, axillary meristems. While the regulation of the stem cell population in an established meristem is well described, how it is initiated in newly formed meristems is less well understood.

De novo stem cell establishment in meristems requires repression of organ boundary cell fate.

Stem cells play important roles in animal and plant biology, as they sustain morphogenesis and tissue replenishment following aging or injury. In plants, stem cells are embedded in multicellular structures called meristems. The formation of new meristems is essential for the plastic expansion of the highly branched shoot and root systems.

Hydathodes.

Bellenot et al. introduce hydathodes, an oft-overlooked plant organ that acts as a pressure valve to expel excess guttation sap at the leaf margin, typically visible at dawn.

A cell wall-associated gene network shapes leaf boundary domains.

Boundary domains delimit and organize organ growth throughout plant development almost relentlessly, building plant architecture and morphogenesis. Boundary domains display reduced growth and orchestrate development of adjacent tissues in a non-cell-autonomous manner. How these two functions are achieved remains elusive despite the identification of several boundary-specific genes.

Meristem Initiation and Stem Cell Formation.

Plant aerial development relies on meristem activity which ensures main body plant axis development during plant life. While the shoot apical meristem (SAM) formed in the embryo only contributes to the main stem, the branched structure observed in many plants relies on axillary meristems (AMs) formed post-embryonically. These AMs initiate from a few cells of the leaf axil that retain meristematic characteristics, increase in number, and finally organize into a structure similar to the SAM.

Photocontrol of Axillary Bud Outgrowth by MicroRNAs: Current State-of-the-Art and Novel Perspectives Gained From the Rosebush Model.

Shoot branching is highly dependent on environmental factors. While many species show some light dependence for branching, the rosebush shows a strict requirement for light to allow branching, making this species an excellent model to further understand how light impinges on branching. Here, in the first part, we provide a review of the current understanding of how light may modulate the complex regulatory network of endogenous factors like hormones (SL, IAA, CK, GA, and ABA), nutrients (sugar and nitrogen), and ROS to control branching.

Mangroves in the Leaves: Anatomy, Physiology, and Immunity of Epithemal Hydathodes.

Hydathodes are organs found on aerial parts of a wide range of plant species that provide almost direct access for several pathogenic microbes to the plant vascular system. Hydathodes are better known as the site of guttation, which is the release of droplets of plant apoplastic fluid to the outer leaf surface. Because these organs are only described through sporadic allusions in the literature, this review aims to provide a comprehensive view of hydathode development, physiology, and immunity by compiling a historic and contemporary bibliography.

Dissecting the pathways coordinating patterning and growth by plant boundary domains.

Boundary domains play important roles during morphogenesis in plants and animals, but how they contribute to patterning and growth coordination in plants is not understood. The CUC genes determine the boundary domains in the aerial part of the plants and, in particular, they have a conserved role in regulating leaf complexity across Angiosperms. Here, we used tooth formation at the Arabidopsis leaf margin controlled by the CUC2 transcription factor to untangle intertwined events during boundary-controlled morphogenesis in plants.

Heterogeneity and its multiscale integration in plant morphogenesis.

Heterogeneity is observed at all levels in living organisms, but its role during the development of an individual is not well understood. Heterogeneity has either to be limited to ensure robust development or can be an actor of the biological processes leading to reproducible development. Here we review the sources of heterogeneity in plants, stress the interplay between noise in elementary processes and regulated biological mechanisms, and highlight how heterogeneity is integrated at multiple scales during plant morphogenesis.

Getting leaves into shape: a molecular, cellular, environmental and evolutionary view.

Leaves arise from groups of undifferentiated cells as small primordia that go through overlapping phases of morphogenesis, growth and differentiation. These phases are genetically controlled and modulated by environmental cues to generate a stereotyped, yet plastic, mature organ. Over the past couple of decades, studies have revealed that hormonal signals, transcription factors and miRNAs play major roles during leaf development, and more recent findings have highlighted the contribution of mechanical signals to leaf growth.

GDP-L-fucose is required for boundary definition in plants.

The CUP-SHAPED COTYLEDON (CUC) transcription factors control plant boundary formation, thus allowing the emergence of novel growth axes. While the developmental roles of the CUC genes in different organs and across species are well characterized, upstream and downstream events that contribute to their function are still poorly understood. To identify new players in this network, we performed a suppressor screen of CUC2g-m4, a line overexpressing CUC2 that has highly serrated leaves.

Multiscale quantification of morphodynamics: MorphoLeaf software for 2D shape analysis.

A major challenge in morphometrics is to analyse complex biological shapes formed by structures at different scales. Leaves exemplify this challenge as they combine differences in their overall shape with smaller shape variations at their margin, leading to lobes or teeth. Current methods based on contour or on landmark analysis are successful in quantifying either overall leaf shape or leaf margin dissection, but fail in combining the two.

Alternate wiring of a KNOXI genetic network underlies differences in leaf development of A. thaliana and C. hirsuta.

Two interrelated problems in biology are understanding the regulatory logic and predictability of morphological evolution. Here, we studied these problems by comparing Arabidopsis thaliana, which has simple leaves, and its relative, Cardamine hirsuta, which has dissected leaves comprising leaflets. By transferring genes between the two species, we provide evidence for an inverse relationship between the pleiotropy of SHOOTMERISTEMLESS (STM) and BREVIPEDICELLUS (BP) homeobox genes and their ability to modify leaf form.

A conserved role for CUP-SHAPED COTYLEDON genes during ovule development.

The evolution of plant reproductive strategies has led to a remarkable diversity of structures, especially within the flower, a structure characteristic of the angiosperms. In flowering plants, sexual reproduction depends notably on the development of the gynoecium that produces and protects the ovules. In Arabidopsis thaliana, ovule initiation is promoted by the concerted action of auxin with CUC1 (CUP-SHAPED COTYLEDON1) and CUC2, two genes that encode transcription factors of the NAC family (NAM/ATAF1,2/CUC).

An APETALA3 homolog controls both petal identity and floral meristem patterning in Nigella damascena L. (Ranunculaceae).

Flower architecture mutants provide a unique opportunity to address the genetic origin of flower diversity. Here we study a naturally occurring floral dimorphism in Nigella damascena (Ranunculaceae), involving replacement of the petals by numerous sepal-like and chimeric sepal/stamen organs. We performed a comparative study of floral morphology and floral development, and characterized the expression of APETALA3 and PISTILLATA homologs in both morphs.